MUSCLE ASPARTYL PROTEASE (CATHEPSIN-D) ACTIVITY - DETECTION USING A CHROMOPHORIC SUBSTRATE AND RELATION TO WASTING IN DBA 2 MICE IMPLANTED WITH LEUKEMIC L1210 TUMOR-CELLS/

The relationship between skeletal muscle aspartyl protease activity (A PA) and wasting was investigated in male DBA/2 mice inoculated with L1 210 tumor cells. Using the peptidic substrate H-Pro-Thr-Glu-Phe-Phe(NO 2)-Arg-Leu-OH, which is specific for aspartyl proteases, proteolytic a ctivity was detected in a number of tissues including muscle by using a crude extraction procedure for isolation of lysosomal enzymes. Bioch emical characterization and increased muscle levels following either f asting or injection of endotoxin (ETX) suggest that the enzyme is like ly cathepsin D. The wasting syndrome accompanying the tumor was measur ed by comparing the weight of the skinned hind limb in treated and con trol animals. DBA/2 mice inoculated intraperitoneally with L1210 cells developed multiple solid tumors in the peritoneum and ascites; maxima l tumor burden was reached by 16 days. There was a significant reducti on in hind limb weight (16 +/- 2%; mean +/- SE) and significant increa se (31 +/- 8%) in muscle APA associated with the development of ascite s and solid tumors. Plasma APA activity was substantially increased (2 40 +/- 33%), while liver and spleen APA were increased (10-20%) but no t significantly. Chronic pepstatin administration, 30 mg . kg(-1). day (-1), for 7 days concurrent with the initiation of observable ascites and solid tumor formation (7 days post-inoculation), completely inhibi ted hind limb weight loss and alleviated the tumor-dependent increase of APA in both plasma and muscle without altering tumor development. D elaying the administration of pepstatin by 3 days resulted in less of an inhibition (33 +/- 13%) of hind limb weight loss. Thus, cathepsin D or a similar aspartyl protease appears to be of key importance in the wasting syndrome associated with cachexia.